Solar Parallax

STOP

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562

SCIENCE.

With the facts that are known in regard to the clinical
history of diphtheria and those which we have deter-
mined in our research, it is easy to make out a theory of
the disease which reconciles all existing differences of
opinion and seems to be true.

A child gets a catarrhal angina or trachitis. Under
the stimulation of the inflammation products the inert
micrococci in the mouth begin to grow ; and, if the con-
ditions be favorable, the sluggish plant may be finally
transformed into an active organism, and a self-generated
diphtheria results. It may be, however, that by ap-
propriate treatment such a case is arrested before
it fairly passes the bounds of an ordinary sore throat.
Every practitioner knows that such diversity does
exist. Again, conditions outside of the body favor-
ing the passage of inert into active micrococci may exist,
and the air at last become well loaded with organisms,
which, alighting upon the tender throats of children,
may begin to grow and themselves produce violent an-
gina, trachitis, and finally fatal diphtheria.

In the first instance we have endemic diphtheria as we
see it in Philadelphia ; in the second, the malignant epi-
demic form of the disease as it existed in Ludington. It
is also apparent that in the endemic cases the plant
whose activity has been developed within the patient
may escape with the breath, and a second case of diph-
theria be produced by contagion. It is also plain that as
the plant gradually in such a case passes from the mild
to the active state, there must be degrees of activity in
the contagium, one case being more apt to give the dis-
ease than is another ; also that the malignant diphtheria
must be more contagious than the mild endemic cases.
We think there is scarcely a practitioner who will not
agree that clinical experience is in accord with these log-
ical deductions from our experimentally determined
premises.

It yet remains for us to investigate as to what are the
conditions outside of the body which will especially
favor the production of active micrococci, and also to
study the effects of agents in killing these organisms ;
for it is very apparent that local treatment of the throat
must often be of the utmost importance, and that it will
be far more effective if it be of such character as to kill
the micrococci, and not simply be anti-phlogistic in its
action.

m

SOLAR PARALLAX.

In an elaborate paper, given in full in the American
Journal of Science, for November, Professor William
Harkness draws the following conclusions : —

For convenience of reference the limiting values of
the solar parallax, found by the various methods de-
scribed in the foregoing pages, are presented here. It
should be remarked, however, that in selecting these
values the results of all discussions made prior to 1857
have been omitted ; except in the case of the transit of
1761, and the smaller of the two values from the transit
of 1769.

I. — Trigonometrical methods.

Mars, meridian observations 8". 84 — 8".g6

" diurnal observations 8.60 — 8.79

Asteroids 8.76 — 8.88

Transit of Venus, 1761 8.49 — io.xo

1769.. 8.55 — 8.91

1874 8.76— 8.85

II. — Gravitational methods.

Mass of the earth 8".87 ± o".o7

Parallactic Inequality 8.78 — 8.91

Lunar Inequality 8.66 — 9.07

III. — Photo-tachymetrical methods.

Velocity and light equation 8". 72 — 8".89

Velocity and Aberration 8.73 — 8.90

To obtain a definite value of the solar parallax, it
would now be necessary to form equations of condition
embodying the relations between the various elements in-
volved ; to weight these equations ; and to solve for it
by the method of least squares. But what is the use?
It is perfectly evident that by adopting suitable weights,
almost any value from 8".8 to 8".9 could be obtained,
and no matter what the result actually was, it would al-
ways be open to a suspicion of having been cooked in
the weighting. We only know that the parallax seems
to lie between 8".75 and 8".90, and is probably about
8". 85. Attack the problem as we will, the results clus-
ter around this central value. All the methods give a
probable error of about ±o".o6, and no one of them
seems to possess decided superiority over the others.
We have nearly exhausted the powers of our instru-
ments, and further advance can only be made at the
cost of excessive labor.

In the beginning of the eighteenth century the uncer-
tainty of the solar parallax was fully two seconds ; now
it is only about o".i5. To narrow it still further, we re-
quire a better knowledge of the masses of the earth and
moon, of the moon's parallactic inequality, of the lunar
equation of the earth, of the constants of nutation and
aberration, of .the velocity of light, and of the light
equation. All these investigations can be carried on at
any time, but there are others equally important which
can only be prosecuted when the planets come into the
requisite positions. Among the latter are observations
of Mars when in opposition at its least distance from the
earth, and transits of Venus.

In 1874 all astronomers hoped and believed that the
transit of Venus which occurred in December of that
year would give the solar parallax within o".oi. These
hopes were doomed to disappointment, and now, when
we are approaching the second transit of the pair, there
is less enthusiasm than there was eight years ago. Nev-
ertheless the astronomers of the twentieth century will
not hold us guiltless if we neglect in any respect the
transit of 1882. Observations of contacts will doubt-
less be made in abundance, but our efforts should not
cease with them. We have seen that the probable error
of a contact observation is ±o".i5, that there may always
be a doubt as to the phase observed, and that a passing
cloud may cause the loss of the transit. On the other
hand, the photographic method cannot be defeated by
passing clouds, is not liable to any uncertainty of inter-
pretation, seems to be free from systematic errors, and is
so accurate that the result from a single negative has a
probable error of only ±0".$$. If the sun is visible for
so much as fifteen minutes during the whole transit,
thirty-two negatives can be taken, and they will give as
accurate a result as the observation of both internal con-
tacts. In view of these facts, can it be doubted that the
photographic method offers as much accuracy as the
contact method, and many more chances of success ?

The transit of 1882 will not settle the value of the solar
parallax, but it will contribute to that result, directly as a
trigonometrical method, and indirectly through the grav-
itational methods with which the final solution of the
problem must rest. As our knowledge of the earth's
mass may be made to depend upon quantities which con-
tinually increase with the time, it will ultimately attain
great exactness, and then the solar parallax will be known
with the same exactness. Long before that happy day
arrives the present generation of astronomers will have
passed over to the silent majority, but not without the
satisfactien of knowing that their labors will contribute
to that fullness of knowledge which shall be the heritage
of their successors.